1. Field of the Invention
The present invention relates to a power factor correction circuit to deal with restrictions for high frequencies and ENERGY STAR requirements for a single voltage power source (AC/DC).
2. Description of the Related Art
FIG. 1 is a circuit diagram illustrating an AC-DC converter including a power factor correction circuit according to a related art. In FIG. 1, the AC-DC converter has a rectifier 103 to rectify an AC input voltage from an AC power source into a rectified voltage, a step-up chopper 104 to step up the rectified voltage, and a DC-DC converter 105 to convert the stepped-up voltage into a stabilized DC voltage.
The AC-DC converter also has a PWM circuit 106, a one-shot multivibrator 107, a pulse synthesizer 108, and a comparator 109.
The PWM circuit 106 generates a pulse signal Vpa according to an output voltage from the DC-DC converter 105 and provides the pulse signal Vpa as a first pulse signal to the one-shot multivibrator 107 and pulse synthesizer 108.
Based on the pulse signal Vpa from the PWM circuit 106 and a delay pulse VpD from the one-shot multivibrator 107, the pulse synthesizer 108 generates a pulse signal Vpb whose pulse width is narrower than the pulse width of the pulse signal Vpa by the pulse width of the delay pulse VpD.
The comparator 109 compares a stepped-up voltage V0 from the step-up chopper 104 with a reference voltage Vref, and if V0 is smaller than Vref, stops the generation of the delay pulse VpD.
This related art is disclosed in Japanese Unexamined Patent Application Publication No. H07-135774.